Saturday, October 20, 2007

Why does salt water taste salty?

In case this burning question was ever bothering you, I thought I'd post the answer here. We have been doing some research on this here at Chez McGrew lately after I noticed in Middle Daughter's science book a diagram that seemed to mean that when salt dissolves in water the ions of chlorine and sodium actually get separated from each other and surrounded by water molecules. So, I wondered, why is dissolving salt in water still considered a physical rather than a chemical change (if the salt is really broken down into its sub-molecular components), why does the salt water still have the property of being salty to the taste, and why do you get the salt back when you reverse the process by evaporating the water?

The answer is apparently that there are such things as semi-associated states of ionic molecular compounds. Evidently the ions of chlorine and sodium are, despite being separated and individually surrounded by water, still associated within a certain distance by their respective charges. This allows them to snap back together into a crystalline solid state when the water is evaporated.

To make things even more interesting, evidently our subjective sensation of a salt taste is caused by the separate effect on our taste buds of the sodium and chlorine ions, not by a single undivided molecular substance called "salt." Hence a certain amount of dissolving actually has to take place in order for us to taste salt at all.

It's my impression that not all compounds (e.g., not sugar) dissolve to this extent in water, but salt is one that does.

See here and here for a Q and A about this.

Now, didn't you always want to know that?


William Luse said...

Personally, I found it fascinating. I eat a lot of salt and never wondered why it tasted that way. But now I know the answer to a question that always mystified me as a kid. What happened to the salt after it dissolved the slug I poured it on? (More than one, actually.)

Lydia McGrew said...

Does salt really dissolve slugs?

Ewwwwww. :-)

William Luse said...

You never poured salt on a slug? Sheltered life.

Tracy:D said...

Actually, this is exactly what I was searching for. lol Thanks!

Anonymous said...

It's funny I just read that when salt was dissolved that it broke down to its ions. Instantly my next question was "so why does it still taste salty." Thank you for providing me with the answer half a decade ago in the past :)

Jenny said...

This was exactly what I was searching for too, after diagramming dissolving salt ready for my class! I had guessed the answer but it's nice to know someone agrees with me!

Anonymous said...

I teach middle school science, and while preparing a lesson I always try to anticipate student questions so that I can research the answers and avoid looking stupid. This was the first question that came to mind, and your wonderfully concise answer hit the spot. Thanks!